import java.util.Scanner;

public class demo01 {
    //年会抽奖
    public static void main(String[] args) {
        long[] arr=new long[21];
        arr[0]=0;
        arr[1]=0;
        arr[2]=1;
        long[] num=new long[21];
        num[0]=1;
        num[1]=1;
        num[2]=2;
        for (int i = 3; i < 21; i++) {
            arr[i]=(i-1)*(arr[i-1]+arr[i-2]);
            num[i]=i*num[i-1];
        }
        Scanner sc=new Scanner(System.in);
        while (sc.hasNext()){
            int n=sc.nextInt();
            double m=100.0*arr[n]/num[n];
            System.out.printf("%.2f%",m);
        }
    }
}
